Hydrocarbons, such as oil and gas, are commonly obtained from subterranean formations that may be located onshore or offshore. The development of subterranean operations and the processes involved in removing hydrocarbons from a subterranean formation typically involve a number of different steps such as, for example, drilling a wellbore at a desired well site, treating the wellbore to optimize production of hydrocarbons, and performing the necessary steps to produce and process the hydrocarbons from the subterranean formation.
Wellbores are created for a variety of purposes, including exploratory drilling for locating underground deposits of different natural resources, mining operations for extracting such deposits, and construction projects for installing underground utilities. Wellbores are often drilled vertically through a subterranean formation. However, in many applications it is desirable to drill wellbores that have vertically deviated or horizontal geometries. A well-known technique employed for drilling horizontal, vertically deviated, and other complex boreholes is directional drilling. Directional drilling is generally typified as a process of boring a hole which is characterized in that at least a portion of the course of the bore hole in the earth is in a direction other than strictly vertical—i.e., the axes make an angle with a vertical plane (known as “vertical deviation”), and are directed in an azimuth plane.
Various options are available for providing steering capabilities to a drilling tool for controlling and varying the direction of the wellbore. For example, directional drilling may also be accomplished with a “rotary steerable” drilling system wherein the entire drill pipe string is rotated from the surface, which in turn rotates the bottom hole assembly (BHA), including the drilling bit, connected to the end of the drill pipe string. In a rotary steerable drilling system, the drilling string may be rotated while the drilling tool is being steered either by being pointed or pushed in a desired direction (directly or indirectly) by a steering device. Some rotary steerable drilling systems include a component which is non-rotating relative to the drilling string in order to provide a reference point for the desired direction and a mounting location for the steering devices. Other rotary steerable drilling systems may be “fully rotating”. Rotary steerable drilling systems can provide relatively high steering accuracy for directional drilling operations.
Directional drilling typically involves controlling and varying the direction of the wellbore as it is being drilled. Oftentimes the goal of directional drilling is to reach a position within a target subterranean destination or formation with the drill string. Downhole sensors in the rotary steerable system can be used to evaluate the formations being drilled through, in order to determine what changes in direction of the rotary steerable tool should be made. Some downhole tools utilize gamma detection sensors that are designed to measure an amount of natural gamma radiation emitted from a subterranean formation. Such information can be useful since pay-zones and formations containing oil will oftentimes emit more gamma radiation than less productive formations. Unfortunately, gamma detection sensors are often housed in non-rotating parts of the drill string, or located far above the drill bit, making it difficult to base quick directional decisions on the sensed gamma radiation.